In the manufacture of multilayer composite panels, it is desirable to temporarily clamp the layers together preliminary to gluing or permanent fastening. This may be done with reusable temporary fasteners which have splayed hook clamps such as Clecos.TM.. A small hole is drilled through all the laminate layers and the clamp is inserted through it. Clamping pressure is applied by tightening a screw which extends a pin between the hooked wires of the clamp to separate them.
A problem with such clamps is consistently obtaining a desired clamping Pressure. Too much pressure may damage laminate layers and too little may result in poor bonding.
One prior art means for limiting the force applied by such clamps is shown in U.S. Pat. No. 3,568,562 to Harwood. Harwood shows an arrangement of a housing, Belleville springs and a force control washer (details 38, 40 and 42) to apply predetermined clamping forces with a reusable temporary fastener. However, this spring and housing arrangement limits the number of clamping pressures which can be applied and is not infinitely variable. Moreover, the force limiting device requires an extra long screw of the Cleco.TM. to accommodate its full length. Variations in laminate thickness also result in different clamp pressures. This can be a serious problem with clamping carbon fiber reinforced laminates which may not have uniform thicknesses.
The subject invention provides a superior force limiting device for reusable temporary fasteners which overcomes the shortcomings of such prior art devices and features a number of other significant advantages which will be described in more detail.